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      2020年3月17日 晚上
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              <h1 id="Eureka-集群原理"><a href="#Eureka-集群原理" class="headerlink" title="Eureka 集群原理"></a>Eureka 集群原理</h1><p>我们假设有三台 Eureka Server 组成的集群，只要三个地方的任意一个Eureka Server不出现问题，都不会影响整个架构的稳定性。</p>
<p><img src="https://s1.ax1x.com/2020/03/19/8yJLwT.jpg" srcset="/blog/img/loading.gif" alt="Eureka集群"></p>
<p>从图中可以看出<code>Eureka Server</code>集群相互之间通过<code>Replicate</code>来同步数据，相互之间不区分主节点和从节点，所有的节点都是平等的。在这种架构中，节点通过<strong>彼此互相注册</strong>来提高可用性，每个节点需要添加一个或多个有效的serviceUrl 指向其他节点。</p>
<p>如果某台Eureka Server 宕机，Eureka Client 的请求会自动切换到新的Eureka Server 节点。当宕机的服务器重新恢复后，Eureka 会再次将其纳入到服务器集群管理之中。当节点开始接受客户端请求时，所有的操作都会进行节点间复制，将请求复制到其它Eureka Server 当前所知的所有节点中。</p>
<p>另外Eureka Server 的同步遵循着一个非常简单的原则：只要有一条边将节点连接，就可以进行信息传播与同步。所以，如果存在多个节点，只需要将节点之间两两连接起来形成通路，那么其它注册中心都可以共享信息。每个Eureka Server 同时也是Eureka Client，多个Eureka Server 之间通过<code>P2P</code>的方式完成服务注册表的同步。</p>
<p>Eureka Server 集群之间的状态是采用异步方式同步的，所以不保证节点间的状态一定是一致的，不过基本能保证最终状态是一致的。</p>
<p>Eureka保证AP (CAP原则又称CAP定理，指的是在一个分布式系统中，一致性(Consistency)、可用性(Availability)、分区容错性(Partition tolerance))</p>
<p>Eureka Server 各个节点都是平等的，几个节点挂掉不会影响正常节点的工作，剩余的节点依然可以提供注册和查询服务。而Eureka Client 在向某个Eureka 注册时，如果发现连接失败，则会自动切换至其它节点。只要有一台Eureka Server 还在，就能保证注册服务可用(保证可用性)，只不过查到的信息可能不是最新的(不保证强一致性)。</p>
<a id="more"></a>
<h1 id="Eureka-集群搭建"><a href="#Eureka-集群搭建" class="headerlink" title="Eureka 集群搭建"></a>Eureka 集群搭建</h1><p>新建一个Eureka Server，并修改<code>application.yml</code>文件<br><pre><code class="hljs yml"><span class="hljs-attr">server:</span>
  <span class="hljs-attr">port:</span> <span class="hljs-number">7002</span>

<span class="hljs-attr">eureka:</span>
  <span class="hljs-attr">instance:</span>
    <span class="hljs-attr">hostname:</span> <span class="hljs-string">eureka7002.com</span>
  <span class="hljs-attr">client:</span>
    <span class="hljs-attr">register-with-eureka:</span> <span class="hljs-literal">false</span>
    <span class="hljs-attr">feth-registry:</span> <span class="hljs-literal">false</span>
    <span class="hljs-attr">service-url:</span>
      <span class="hljs-comment"># 相互注册</span>
      <span class="hljs-attr">defaultZone:</span> <span class="hljs-string">http://eureka7001.com:7001/eureka/</span></code></pre></p>
<p>修改之前的单机eureka配置文件<br><pre><code class="hljs yml"><span class="hljs-attr">server:</span>
  <span class="hljs-attr">port:</span> <span class="hljs-number">7001</span>

<span class="hljs-attr">eureka:</span>
  <span class="hljs-attr">instance:</span>
    <span class="hljs-attr">hostname:</span> <span class="hljs-string">eureka7001.com</span>
  <span class="hljs-attr">client:</span>
    <span class="hljs-attr">register-with-eureka:</span> <span class="hljs-literal">false</span>
    <span class="hljs-attr">feth-registry:</span> <span class="hljs-literal">false</span>
    <span class="hljs-attr">service-url:</span>
      <span class="hljs-comment"># 相互注册</span>
      <span class="hljs-attr">defaultZone:</span> <span class="hljs-string">http://eureka7002.com:7002/eureka/</span></code></pre></p>
<blockquote>
<p>因为是在同一台机器上，所以需要修改host文件将<code>eureka7001.com</code>和<code>eureka7002.com</code>映射为<code>127.0.0.1</code></p>
</blockquote>
<h1 id="微服务注册进集群"><a href="#微服务注册进集群" class="headerlink" title="微服务注册进集群"></a>微服务注册进集群</h1><p>回到之前的子工程中，修改<code>application.yml</code>文件中的eureka配置<br><pre><code class="hljs yml"><span class="hljs-attr">eureka:</span> <span class="hljs-comment"># eureka 客户端</span>
  <span class="hljs-attr">client:</span>
    <span class="hljs-attr">register-with-eureka:</span> <span class="hljs-literal">true</span>
    <span class="hljs-attr">fetch-registry:</span> <span class="hljs-literal">true</span>
    <span class="hljs-attr">service-url:</span>
      <span class="hljs-comment"># 服务中心链接</span>
      <span class="hljs-attr">defaultZone:</span> <span class="hljs-string">http://eureka7001.com:7001/eureka,http://eureka7002.com:7002/eureka</span></code></pre></p>
<p>启动服务，查看是否正确<br><img src="https://s1.ax1x.com/2020/03/19/8y5eZ6.png" srcset="/blog/img/loading.gif" alt="集群"></p>

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